This invention relates to the treatment of water, such as, for example, municipal or industrial waste water, or river or lake water. This invention is especially useful in the purification of water to a very high degree such as for potable water.
Commonly surface waters such as lake or river water, or subterranean water is treated for use as potable water. These waters often contain materials which can cause bad taste or odor, or other harmful substances. Some of these substances are organic from decaying vegetation, such as humic acids. Other substances are from various agricultural or industrial application, such as aromatics, phenolics, and the like.
Potable water is commonly purified by treating the water with chemicals and activated carbon. The water is contacted with powdered activated carbon and chemicals such as alum and polyelectrolytes, and then passed to a flocculation zone where the mixture is gently mixed so as to promote flocculation while not unduly dispersing solids. The mixture is then passed to a clarification zone where sludge is disposed of, generally without the recovery of the alum. Sometimes the purified water is then contacted with carbon in a fixed bed granular carbon zone for a final clean up. Previously, the activated carbon has had relatively low activity and surface area. Also, the water purification processes have not made the best use of carbon on a per gallon of treated waste water basis.
Commonly waste water from industrial sources such as refineries, chemical plants, wood processing, food processing, and the like, and from municipal sources requires treatment in order to make it environmentally acceptable. The treatment of contaminated waste water from municipal or industrial sources involves a sequence of processing steps for maximizing water purification at minimum costs. Industrial effluents, particularly waste water from oil refineries, include a broad spectrum of contaminants, and, consequently, such waste water is usually more difficult to decontaminate than waste water from municipal sewage systems. Four main sequential process treatments are used to decontaminate such industrial effluents although similar treatment is given municipal effluents, or combined municipal/industrial effluents. These are a primary, intermediate, secondary, and tertiary treatments. The primary treatment calls for removal of gross amounts of oil and grease and solids from the waste water. In the oil industry, usually separators of American Petroleum Institute design are employed for removal of free, separable oil and solids. In municipal waste water treatment, generally little free oil is present but solids removal is still needed. The intermediate treatment is the next process and it is designed to adjust water conditions so that the water entering the secondary treatment zone will not impair the operation of the secondary treatment processes. In other words, intermediate treatment is designed to optimize water conditions so that the secondary treatment process will operate most efficiently. The secondary treatment calls for biologically degrading dissolved organics and ammonia in the water. One of the most common biological treatment processes employed is the activated sludge process discussed below in greater detail. The tertiary treatment calls for removing residual biological solids present in the effluent from the secondary treatment zone and removing contaminants which contribute to impairing water clarity or adversely affecting water taste and odor. This is usually a filtration of the water, preferably through beds of sand, or combinations of sand and coal, followed by treatment with activated carbon.
The activated sludge process is a conventional waste water treating process which produces the highest degree of biological treatment in reasonably compact facilities at the present time. The application of this process to the treatment of industrial waste water has, however, been slow compared with municipal applications. Industrial applications of this process are nevertheless increasing rapidly. Often the BOD.sub.5 contaminants present in industrial waste water are relatively small compared with the total oxygen demanding contaminants present in such waste water as measured by the chemical oxygen demand (COD) test. For example, the BOD.sub.5 contaminants present in the effluent from an activated sludge process typically ranges from 10 to 20 parts per million parts of water. It is not uncommon to also find present in such effluent 10 to 20 times this amount of COD.
The activated sludge process generally has at least two, preferably four stages of treatment. In the first stage, contaminated water is contacted with the activated sludge. The sludge includes micro-organisms which feed on the contaminants in the water and metabolize these contaminants to form cellular structure and intermediate products. This decontaminated water flows into a second clarifier stage where suspended sludge particles are separated from the decontaminated water. A portion of the sludge is recycled to the first stage and the remainder can be forwarded to the third and fourth stages as is taught in U.S. Ser. No. 657,497, filed Feb. 12, 1976. This sludge forwarded to the third and fourth stages includes water. In the third stage the sludge is thickened to remove excess water and in the fourth stage the thickened sludge is permitted to digest, that is, the micro-organisms feed upon their own cellular structure and are stabilized. Normally, the average age of these micro-organisms in the sludge is substantially less than ten days.
Activated carbon is sometimes used in tertiary treatment as a final clean up for purified water from the second stage clarifier. Some have taught that activated carbon or Fuller's earth can be used to treat waste water in a biological treatment process. U.S. Pat. No. 3,904,518 teaches that between about 50 and 1500 parts of activated carbon or between about 250 and 2500 parts of absorptive Fuller's earth per million parts of feed waste water can be beneficial in water purification. The carbon or Fuller's earth has a surface area of at least 100 square meters per gram and the activated carbon usually can have a surface area of between 600-1400 square meters per gram. However, the use of this relatively large amount of carbon is expensive and therefore it has not been widely used. Also, the carbon has a relatively low activity and surface area.
The conventional scheme of waste water treatment may not be able to meet the stringent water quality standards of the future. Therefore, a process for further purification of partially purified waste water is needed.
It is an object of this invention to provide an improved water treatment process and an improved waste water treatment process.
It is an object of this invention to provide an economical method of treating waste water through the efficient use of powdered activated carbon.
It is an object of this invention to provide a process for the production of potable water or water having a very high purity.
It is an object of this invention to provide an integrated waste water treatment scheme for the purification of water to very high levels of purity.